Phosphites have been found to be extremely effective in the control of diseases particularly those that belong to the Oomycetes group such as Phytophthora spp., Pythium spp., and the Downy Mildew diseases.  In addition to these, phosphites also control some fungal diseases that fall outside this group such as Venturia inaequalis (Apple Scab) and some bacterial diseases such as Erwinia amylovora (Apple Fireblight).  

The Phosphite Story